Pressure-Induced Comproportionation in Palladium Trifluoride

Despite its seeming simple stoichiometry, palladium trifluoride (PdF₃) is a mixed-valent system better formulated as Pd^IIPd^IVF₆. In an attempt to verify whether the application of high pressure (P > 1 GPa) might force this compound to form a genuine palladium(III) fluoride (Pd^IIIF₃), a joint theoretical and experimental study on its properties at large compression was performed. Indeed, hybrid density functional calculations predict the thermodynamic preference for single-valent (comproportionated) polymorphs at pressures exceeding 30 GPa. The ambient-pressure LiSbF₆-type polymorph of R3̅ symmetry was experimentally observed to transform into a triclinic P1̅ phase above 42 GPa. While this polymorph is still a mixed-valent compound Pd^IIPd^IVF₆, another phase transition, commencing at ∼50 GPa, introduces a monoclinic C2/c phase containing genuine Pd^III centers. Both high-pressure polymorphs of palladium trifluoride exhibit novel structure types. Moreover, preliminary data suggest that the C2/c comproportionated structure might host strong one-dimensional antiferromagnetic exchange interactions.

Palladium trifluoride is derived from a mixed-valent state (Pd^IIPd^IVF₆) into a phase exhibiting a single palladium valency (Pd^IIIF₃) under high pressure, as shown through a combination of diamond anvil cell experiments (Raman spectroscopy, powder X-ray diffraction) and hybrid DFT calculations.